Quinoline lithium aluminum hydride reduction

Reduction of quinoline with lithium aluminum hydride gives 1,2-dihydroquinoline. Neutral pyridines bearing electron-withdrawing substituents are also reduced by sodium borohydride (Scheme 32). 

Numerous reducing agents were tried at this point unsuccessfully. For example, lithium aluminum hydride destroyed the substrate, whereas DIBAH or lithium borohydnde in THF and sodium borohydride in ethanol led to reduction of the quinoline system. On the other hand, both potassium borohydride (either with or without 18-crown-6) and zinc borohydride (with or without ethanol) produced no reaction at all. Lithium triethylborohydride resulted in de-methoxylation, and sodium borohydride in refluxing THF gave a 45% yield of diol 16 together with overreduced product. 

The reduction of quinolinium salts or quinolines with lithium aluminum hydride gives predominantly the 1,2-dihydroquino-lines.78,92, 95- 97-103 The yield of product appears to depend upon the... 

In contrast to the quinoline and isoquinoline series, thienopyridines are apparently resistant to reduction by tin-hydrochloric acid, since the parent systems can be obtained by reductive dehalogenation or chloro-derivatives. Quaternary salts are reduced to the JV-alkyl-4,5,6,7-tetra-hydrothienopyridine by sodium borohydride,45,48,89-91 and the azo-methine bond in dihydro derivatives (e.g. 69) is reduced by lithium aluminum hydride.47... 

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